At first thought, it may seem like good sleep is the enemy of an active social life. The more time you dedicate to catching zzzs, theoretically, the less is left for socializing. And it would follow that the most vibrant social butterflies of the bunch may not be the ones clocking their optimal hours of slumber nightly. But as it turns out, sleep and socializing are good friends: The more well-slept you are, the more likely you are to engage socially and to give and feel connected to others; whereas, sleep loss causes social withdrawal and loneliness.

These findings are part of a growing body of research connecting the dots between sleep health and social health. While studies have correlated sleep troubles and loneliness for some time, it’s long been a chicken-and-egg issue, where it wasn’t clear which came first.

Recent research analyzing the effect of loneliness on our ability to get quality sleep has found that lonelier folks do, indeed, experience more sleep fragmentation (aka awakenings throughout the night). “You need to feel safe and secure to sleep well, and feeling lonely or like you have fewer connections could make you feel subconsciously less secure and therefore, negatively influence your sleep quality,” says epidemiologist Diane S. Lauderdale, PhD, chair of the Department of Public Health Sciences at The University of Chicago.

But now, we also know that, on the flip side, getting poor sleep can cause antisocial behaviors and leave you feeling more lonely overall. Which is to say, loneliness or sleep loss can kick off a vicious cycle that involves both, and the relationship between the two is bidirectional.

“We’re learning now that the health of social relationships depends on good sleep.” —Eti Ben Simon, PhD, neuroscientist and sleep researcher

Understanding poor sleep not just as a symptom of loneliness, but as a trigger of it, reinforces what we are continuing to learn about sleep: It has a powerful influence on health. “Up to this point, we’ve focused on the individual mental and physical health of the person getting or losing sleep—and that makes sense, since we needed to start with the obvious,” says neuroscientist Eti Ben Simon, PhD, sleep researcher at the Center for Human Sleep Science at the University of California Berkeley. “But we’re learning now that the health of social relationships also depends on good sleep.”

How sleep loss causes social withdrawal and decreases feelings of connection with others

To study whether being sleep-deprived would affect people’s willingness to engage socially, Dr. Simon and her colleague, neuroscientist Matthew Walker, PhD, organized an experiment where 18 participants stood face-to-face with one of the researchers who slowly walked toward them with a neutral expression. The participants—who were sleep-deprived during one instance of this experiment and had a full night’s rest on the other—were tasked with telling the researcher to stop walking toward them whenever they felt like they were getting too close.

In every case, people kept the researcher significantly farther away (from 18 to 60 percent farther) when they were sleep-deprived than when they weren’t, reflecting a decreased desire to interact with others while in a sleep-deprived state, says Dr. Simon.

Curious as to whether people actually feel less socially connected after a night of poor sleep, the researchers also conducted a remote study where more than 100 participants slept however they chose for two nights, and then answered questions on the following days about their sleep, as well as questions designed to parse how lonely they felt, like, “How often do you feel isolated from others?” and “Do you feel like you don’t have anyone to talk to?”

“The reason we designed the test like this is because, while social isolation and loneliness are related, the concept of loneliness is subjective,” says Dr. Simon. “It has to do with whether you feel like you are socially connected to others who understand and support you.” As it turned out, those participants who reported a worse night of sleep on the second night of the study also showed higher markers of loneliness on the day to follow than they had on the day prior.

To make matters worse, this sleep-deprived state isn’t exactly conducive to reaching out to a friend as a way to quell that loneliness. A study for which more than 600 people maintained a daily sleep diary and activity log (including markers of how sleepy they felt every three hours) found that feeling sleepy was associated with a substantial dip in the likelihood of doing a social activity. And another study assessing the motivations of more than 100 people to do various activities after either a normal night of sleep or an all-nighter corroborated this result: Those who were sleep-deprived reported significantly less desire to engage in social activities like going on a date or hanging out with a friend.

“There’s something about the need for sleep that is so strong, it seems to push off anything else—and you just want to be alone so you can get that sleep.” —Dr. Simon

Taken together, these studies show that the more sleep you lose, and the sleepier you are the next day, the more lonely you’re likely to feel and the less you’ll want to hang out with anyone. “There’s something about the need for sleep that is so strong, it seems to push off anything else—and you just want to be alone so you can get that sleep,” says Dr. Simon.

Indeed, that feeling of social reluctance can be so intense in a sleep-deprived state of mind that others can sense it and may feel less willing to engage in response. This is what Dr. Simon and Dr. Walker found when they asked about 1,000 people to watch recorded videos of their 18 in-lab participants above (some of whom were sleep-deprived for the taping and others of whom were not) discussing commonplace topics and opinions. Not knowing that the sleep of these participants had been manipulated, the observers repeatedly rated the people in the sleep-deprived state as less socially desirable—as people with whom they wouldn’t want to have a conversation or interaction.

It’s easy to see how this kind of response can set off a negative spiral for your social life, says Dr. Simon: “You start with a lack of sleep, which reduces your desire to be around other people, causing other people to then feel like they want to stay away from you, which can then further increase your social withdrawal and loneliness.” As noted above, such feelings of loneliness can, in turn, worsen your sleep quality, starting the whole cycle over again.

Why sleep deprivation has such a negative effect on our social relationships

When you’re lacking sleep, your body’s sole focus is…to get sleep. While, at a conscious level, you may then choose to pass on social activities or hangouts, some of that decision-making around social withdrawal happens at a subconscious level.

In particular, sleep deprivation seems to “turn off” or dial down parts of the brain that have to deal with thinking about other people, says Dr. Simon. “There are brain regions known as the ‘theory of mind‘ network that are typically active when we think about other people and consider what they are like, what they might want, how they are similar or different to us, and so on,” she says. When she and Dr. Walker used fMRI scans to assess the brain activity of the 18 participants in their sleep and social withdrawal study, they found that when the participants were sleep-deprived, their “theory of mind” networks were significantly less active.

This yields an interesting rationale for why sleep loss causes such social withdrawal and loneliness: When we’re tired, our brains have an impaired ability to consider other people and perspectives. “It’s not that when we’re sleep-deprived, we’re ignoring people or we just don’t care, but perhaps at a more basic level, it’s just harder in that state for us to even think about what others might want or need,” says Dr. Simon.

In other words? Sleep loss seems to make our brains, to some degree, more selfish or self-centered. This finding has also been borne out in studies analyzing the impact of sleep loss on particular kinds of social interactions requiring empathy, sympathy, and generosity: Sleepy people were categorically less likely to engage in these behaviors—which makes sense if their brains are only focused on themselves.

For instance, Dr. Simon conducted a study to determine how one night of sleep loss affects people’s desire to help others, and 78 percent of participants reported less willingness to help a stranger or someone they knew when in a sleep-deprived state versus when well-rested.

Similarly, in a study assessing how doctors prescribe pain-management during day versus night shifts, researchers found that, during the night shifts, when the doctors were presumably more tired, they tended to under-prescribe pain relievers and reported less empathy for patient pain. And in another study on sleep and interpersonal conflict, researchers found that people in relationships reported more conflict and a decreased ability to resolve conflict following nights of poor sleep.

“We struggle to do anything that involves taking another person’s perspective when we’re sleep-deprived.” —Dr. Simon

What all of this research points to is “the notion that we tend to withdraw from others and struggle to do anything that involves taking another person’s perspective when we’re sleep-deprived,” says Dr. Simon. “We are really not able to leave our own private spheres.” The result is poorer, if any, engagement and communication in social relationships of all sorts.

Good sleep, by contrast, is a social lubricant. “We tend to think, ‘Oh, if I’m going to sleep, I’m going to miss this and I’m going to miss that,” says Dr. Simon. (Cue: major FOMO.) But in actuality, “sleep isn’t a loss for your social life; it’s an investment,” she says. “Once you do get good sleep, you’re much more open, subjectively and objectively, to having people around you, you feel more connected to people, and they feel more connected to you.”